Todd A. Lee, PharmD, PhD; A. Simon Pickard, PhD; David H. Au, MD, MS
Potential Financial Conflicts of Interest:Honoraria: T.A. Lee (AstraZeneca, Novartis), D.H. Au (GlaxoSmithKline). Stock ownership or options (other than mutual funds): D.H. Au (Pfizer). Grants received: T.A. Lee (Altana, Aventis, AstraZeneca, Boehringer Ingelheim, Chiesi, GlaxoSmithKline, Merck & Co., Novartis, Pfizer, Schering-Plough, Sepracor, University of Kentucky). Other: D.H. Au (Assessing the Impact of Recent Updates for Advair and Serevent Special Issues Board).
Lee TA, Pickard AS, Au DH. How Much Did Biases in the Study of Chronic Obstructive Pulmonary Disease Medications and Mortality Affect the Outcome?. Ann Intern Med. 2009;150:426-427. doi: 10.7326/0003-4819-150-6-200903170-00020
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Published: Ann Intern Med. 2009;150(6):426-427.
We thank the correspondents for their thoughtful comments. Drs. Suissa and Ernst raise 3 concerns about our article. First, to alleviate concerns that the observed risk for ipratropium and cardiovascular mortality was a result of an increased risk for exacerbations in the case patients, we conducted an analysis restricted to those without an exacerbation in the 180 days before their event date and found a level of risk (odds ratio, 1.45 [CI, 1.14 to 1.85]) similar to the results reported in the article. Second, unmeasured confounding and bias is a possible explanation for the discordant results between the TORCH study and our study. Among the other explanations, the difference in outcomes may be related to the patient populations. The population included in our analysis was older, had higher overall and cause-specific mortality rates, was nearly all male, had more coexisting conditions, and had differential respiratory medication use before entering the study. Third, we were able to measure medications used in the Veterans Administration health care system during inpatient stays, and thus the analysis was not subject to concerns about immeasurable time bias.
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